1. Field of the Invention
The present invention relates to a connecting rod of an internal combustion engine and, more particularly, to a connecting rod made of a light alloy.
2. Description of the Prior Art
In general, the mechanical strength and shape of the connecting rod of an internal combustion engine are required to meet various requirements in order to sustain buckling and bending forces.
As to the buckling of the connecting rod, the following relationship exists between the strength and the shape of the connecting rod. ##EQU1## where, X and Y are orthogonal axes. More specifically, in the cross-section of the rod portion of the connecting rod, the Y axis extends in the direction parallel to the axis of the piston pin, while the X axis extends at a right angle to the Y axis. Symbols Py and Px represent the buckling load in the Y axis (rotational direction) and the buckling load in the X axis (axial direction). A symbol A represents the critical cross-sectional area of the rod portion. The symbol .sigma.y,x represents the tensile strength in case of a homogeneous material, while a symbol .alpha.o represents a constant. The distance between two axes of small and big ends of the connecting rod is shown at a symbol l. Symbols Iy and Ix designate, respectively, the second moment of inertia in Y axis (rotational direction) and second moment of inertia in X axis.
There also is a relationship expressed by the following equation (1) in which K represents the allowable limit of buckling. EQU P.sub.y .gtoreq.P.sub.x &gt;K (1)
From the equation (1) above, derived is the following equation (2). EQU .sigma..sub.y .multidot.I.sub.y .gtoreq..sub.x .multidot.I.sub.x ( 2)
In case of a homogeneous material, since .sigma.y and .sigma.x are equal to each other, the equation (2) is transformed into the following equation (3). EQU I.sub.y .gtoreq.I.sub.x ( 3)
Thus, the rotary side of a connecting rod is supported materially in the same manner as the free support and tends to buckle easily as compared with the axial side. In addition, the rotary side of the connecting rod is subjected to oscillating bending force. For these resons, it is a common measure to determine that the second moment of inertia be made greater at the rotary side (Y axis) than at the axial side (X axis).
Under these circumstances, it has been recommended to make the rod portion of the connecting rod have an H-shaped cross-section. In such a case, in order to increase the second moment of inertia Iy in the Y axis, it is necessary to locate the mass at as large distance as possible from the Y axis, which in turn increases the size of the connecting rod in X axis. Particularly, in the connecting rod made of a light alloy, it is necessary to select the Iy and Ix having considerably large values, not to mention of the relation of Iy.gtoreq.Ix. In consequence, the size of the connecting rod is X axis is further increased.
The increased size of the connecting rod made of a light metal inevitably widens the locus of the rotation of the connecting rod, resulting in an interference with the cylinder sleeve and with the cylinder block, posing a serious problem concerning the space utilization. This problem is serious particularly in the long stroke engines. Thus, for accommodating a connecting rod made of a light alloy having a sufficient mechanical strength in a space which has been designed for a conventional connecting rod made of a steel, modifications and changes of design are necessary for various parts of the engine. These modifications and changes are materially impossible. Even if the engine as a whole is designed newly for the use of the connecting rod made of a light alloy, there is necessary a large space of the cylinder block. At the same time, there is a restriction to the length of the cylinder. In consequence, the projection length of the piston from the lower part of the cylinder is increased inevitably resulting in an unstabilized piston behaviour. This is unacceptable particularly in the long stroke type engines.
On the other hand, there is an increasing demand for reduced weight and fuel consumption of internal combustion engines, which in turn requires to achieve the reduction of weight of the reciprocating masses in the engine. This gives rise to a demand for the reduction of weight of the connecting rod. Thus, the above stated problems have to be overcome soon, in order to achieve the reduction of weight of the connecting rod.